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Reader Request: Nuclear Fission vs. Nuclear Fusion

A new year, a new claim by North Korea that they’ve successively built and tested a hydrogen bomb (which by the way, may not be true). In light of all this talk about nuclear warfare in the media, one of my readers (hi, Jason!) asked me a really good question:

What isa hydrogen bomb exactly, and how is it different from an atomic bomb?

To answer this, let’s start with the simpler one: the atomic bomb. The atomic bomb is the type of bomb that the Americans infamously used during World War II against the Japanese. An atomic bomb relies on nuclear fission, the splitting of one atom into two, to produce an explosion. In the original atomic bomb, the atom split was uranium-235. To start this process, neutrons (one of the three components that make up an atom*) must be shot into a small mas of uranium-235. When this happens, some of the atoms will absorb a neutron into the center of the atom, the atomic nucleus. After the atomic nucleus absorbs that neutron, it gains energy, begins to fragment, and then splits apart into two new atoms. Importantly, fission also releases more neutrons and gives off a bit of energy. The released neutrons then bombard other uranium-235 atoms within the bomb, causing them to also undergo fission. This essentially initiates a chain-reaction of explosions that, added up, is one gigantic explosion.

Unlike the atomic bomb, a hydrogen bomb uses nuclear fusion to create an even bigger explosion – around 700 times bigger than the explosion produced by the first atomic bomb. Scientifically speaking, nuclear fusion is the exact opposite of fission. Instead of one atom splitting into two new ones, two atoms combine with one another to form a bigger one. This process produces even more energy than fission, and results in a bigger explosion. While the actual design/mechanism of a hydrogen bomb is classified information, the basic principles of how it would work is public knowledge. Rather than splitting uranium-236 into two new atoms, a hydrogen bomb combines atoms of deuterium and tritium (both isotopes of hydrogen) to make helium. The source of deuterium/tritium is known as the “fusion fuel”.

Unlike the atomic bomb, the hydrogen bomb poses some issues:

For nuclear fusion to occur, atoms need to be pushed extremely close to one other. This is difficult because all atoms have positively charged nuclei that will repel each other as they get closer. If you’ve ever tried to push the positively charged sides of two magnets together, you’d know how difficult this is. With enough energy though, you can overcome that repelling force. The problem is that you need a LOT of energy. For hydrogen bombs, that energy is made through nuclear fission. So basically, to set off a hydrogen bomb you need to first set off an atomic bomb.

Tritium is extraordinarily hard to find, and just as hard to keep contained.

The bomb needs to be able to implode a pellet of fusion fuel and simultaneously heat it up to extremely high temperatures.

How to prevent the bomb from accidentally triggering itself.

There are even some issues so complex that only a select few countries have figured out how to solve them. Still, if you would like to venture even deeper into the science behind a hydrogen bomb, then I would recommend checking out this website.

So to summarize, atomic bombs produce explosions through nuclear fission, the splitting of atomic nuclei. In contrast, hydrogen bombs carry out nuclear fusion, or the merging of atomic nuclei. Hydrogen bombs are vastly more complex and harder to build, which is why very few countries are believed to actually own one. Nonetheless, both are extremely catastrophic weapons, and we can only hope they will never be used in any future warfare.

*The three components are electrons, protons, and neutrons. Protons and neutrons are actually themselves, made up of quarks